It wasn't too hard to find a way to game the system:
1) Create a positive tag, publicly available that people will want to associate themselves with.
2) Tag people with it - especially some well know names
3) Once you've built up a good number of people with the tag - Edit the tag so it reflects what you want to market
4) Voila, now you have a group of people associated with your scheme.
I created a tag 'Weekend Tester' as a public tag then found there was a private one called the same. Tag deletion is not yet an option so I decided to change the tag I'd created to something else ( no-one else had yet tagged themselves with it ).
This is when I realised that people who had tagged themselves with a tag could find themselves tagged as something completely different if the tag was changed... maybe "fan of ISEB certification"
Thanks to 007 Unlicensed to Test for helping me illustrate the point. He tagged himself as a Weekend Tester and now finds himself as a fan of this site